This is the final report of a project conducted from February 1, 1990 - March 31, 1991. This paper describes the results of this study that was undertaken as part of an attempt to understand the migration and stock identity of the king and Spanish mackerel in the Gulf of Mexico. The goal was to report length/frequency distributions and catch per unit effort (CPUE) information, to obtain otoliths and adult mackerel specimens for electrophoresis, and to tag Spanish mackerel at specific Mexican locations. These locations were chosen so that the tagging effort would correspond with mackerel migration patterns off Mexico. During 1990, tagging efforts were concentration off the states of Campeche, Yucatan and Veracruz.